Ghost note problem...help!

tonebottle · Post by **tonebottle** » Mon Nov 19, 2007 1:09 pm

I have been battling a "ghost note" problem with my 73' Super Lead. This sounds like an out of tune note or harmonic following the single notes I play. I have read a few threads here, and all of the other info I could get my hands on, and of course, it seems like the classic filter cap problem, but I have just replaced all 6 of the filter caps with new JJs, as well as all the electrolytics I could find on the board (3).

I replaced every tube in the amp with new JJs - a matched quad of EL34Ls, and 3 new 12AX7Ss. I retubed the amp first, and then noticed the problem. I didn't notice it with the old tubes, but I hadn't played the amp for some time, so I can't tell you if it had the problem with them or not. I know the "L" designation tubes have different specs, but don't know how this may effect the filtering, if it would at all. I have not put the old tubes back in to try that, because I just keep thinking if the amp is in good shape otherwise, new tubes of any type would surely not cause a problem like this. ???

I am also wondering if the resistors on 2 of the filter caps may have anything to do with it, or if placing an additional capacitor somewhere may help beef up filtering and stop the symptom. I just can't imagine that this amp in it's stock form, with new caps, would have this problem. My thinking is probably clear out in left field on this, and I just know there's someone out there who can help. I value and appreciate any guidance you can offer.

NitroLiq · Post by **NitroLiq** » Mon Nov 19, 2007 2:06 pm

Did you just replace the filters or did you up the values a bit?

tonebottle · Post by **tonebottle** » Mon Nov 19, 2007 2:50 pm

I just replaced them with the stock values - all 50 X 50's.

NitroLiq · Post by **NitroLiq** » Mon Nov 19, 2007 5:24 pm

You can try to increase the filtering values to get rid of the ghosting. Sometimes it can stiffen up an amp a little...some like it, some don't.

Billy Batz · Post by **Billy Batz** » Mon Nov 19, 2007 6:52 pm

Your at the highest stock values already. Youd have to find some 100/100 cans. They are out there in other amp electronics supply vendors. Getting a higher H and I value choke is supposed to help some as well.

tonebottle · Post by **tonebottle** » Mon Nov 19, 2007 7:06 pm

I see that George sells some 100 X 100 JJ's. Which position caps would I need to replace with these, or would I need to do all of them?

Also, is there a way I could attach some axial caps in parallel to the existing 50s?

BTW - I did switch the old tubes back into the amp a little while ago, and of course, the problem is still there.

toner · Post by **toner** » Mon Nov 19, 2007 7:23 pm

In my experience, the mains filters are the most important for reducing ghosting. You can wire your current 50/50 caps for 100uF or even 200uF but that's pretty drastic.

Removing the resistors from the filter caps can help a little. That was one thing I tried.

Grounding is very important when trouble-shooting ghosting. Check all ground solder joints. You can also un-bolt ground lugs and lightly file the chassis, ground lug tabs and any washers so they make a good contact.

tonebottle · Post by **tonebottle** » Mon Nov 19, 2007 8:58 pm

I just disconnected the resistors, replaced one screw, star washer and nut, sanded a lug and the chassis, and ran some redundent grounds on the filter caps, and it didn't change anything yet. I will keep checking grounds.

I don't know that it would make any difference, but what about having the amp plugged into a wall outlet that was not grounded? I ran a grounded extension cord up to the amp, but it didn't help. I'm wondering now if I should check the main earth ground for my house? I tried the ground switch on the amp in both positions, and no difference. Is my thinking off?

I would be willing to increase the filtering if I can do so with what I already have, just to see if it makes a difference - I just need to know where and how.

planetjimi · Post by **planetjimi** » Mon Nov 19, 2007 9:28 pm

Toner, didn't you got rid of your ghosting by grounding your presence pot to the PI cap lug?

You may want to try that Tonebottle.

toner · Post by **toner** » Mon Nov 19, 2007 9:53 pm

planetjimi wrote:Toner, didn't you got rid of your ghosting by grounding your presence pot to the PI cap lug?

You may want to try that Tonebottle.

Yeah, but some people doubt it was the fix because I also installed a PPIMV at the same time. I can't say that changing the presence pot grounding is a cure all, but I firmly believe it fixed my amp. I tried about everything else and had just learned to live with it until the MV was installed. I've since lowered filtering to '67 specs (still 50uF on mains and screens) and have absolutely no ghosting, even cranked into an attenuator.

I changed the presence ground for two reasons:
1) I put the MV in the presence pot location and moved the presence to the second speaker jack.
2) SDM has an "alternate" grounding scheme that rockstah and others have used successfully which has it grounded that way.

My best guess is that the typical ground buss connection was faulty in my amp. YMMV.

200uF mains WILL get rid of most, if not all ghosting, but the tone and feel just plain sucks, IMO (very sterile and lifeless). That would be a last resort if nothing else works.

tonebottle · Post by **tonebottle** » Mon Nov 19, 2007 10:01 pm

I'll give it a try tomorrow planetjimi. Would this be one of the output coupling caps?

toner · Post by **toner** » Mon Nov 19, 2007 10:11 pm

tonebottle,
Here's a partial quote from a forum member that replied to one of my ghosting posts. It describes wiring the mains caps to 200uF.

Note: Depending on the caps, this may cause problems if your B+ is over 500VDC. I'm not a tech, so please ask others here before trying this with a high B+ voltage.

You can do this easily on a 6 cans up top Marshall if your amp has <500V of B+ and you are using 500V rated filter caps....
Unsolder the yellow Power Transformer centre tap from the middle of the two filter caps and stub it off with some heatshrink and tuck it away. Remove the little wire that connects the -ve of one cap to the +ve's of the other. Then connect the +ve's of both caps together, and the -ve's together too. You are fitting the two cans in parallel instead of series, because one of them has it's +ve connected to B+, the other it's -ve to ground.

You can also try 100uF mains by using only one half of each cap and wiring them in parallel (one positive to one positive of the other cap; negative to the other negative). Leave one positive terminal of each cap disconnected.

Here's a related thread:
http://forum.metroamp.com/viewtopic.php?t=12999

planetjimi · Post by **planetjimi** » Mon Nov 19, 2007 10:32 pm

tonebottle wrote:I'll give it a try tomorrow planetjimi. Would this be one of the output coupling caps?

No, what you want to do is ground the presence pot to the lug of the filter cap in back of the amp. The one by the fuse holders. THAT is the phase inverter "PI" cap.

toner · Post by **toner** » Mon Nov 19, 2007 10:37 pm

tonebottle wrote:I don't know that it would make any difference, but what about having the amp plugged into a wall outlet that was not grounded?

Don't run the amp without a proper ground!!! Regardless of its effect on ghosting, there are serious safety issues from what I understand.

toner · Post by **toner** » Mon Nov 19, 2007 10:41 pm

planetjimi wrote:
tonebottle wrote:I'll give it a try tomorrow planetjimi. Would this be one of the output coupling caps?
No, what you want to do is ground the presence pot to the lug of the filter cap in back of the amp. The one by the fuse holders. THAT is the phase inverter "PI" cap.

Here's SDM's alternate grounding scheme that I mentioned:
http://home.comcast.net/~jbjdav26/1959_R14_alt_grnd.JPG

Look at the black wire from the presence cap that goes to the PI cap ground in the upper-right corner.

The output couplers are not involved.